I. Field of the Invention
This invention relates to communications system interface circuits and more particularly to interface circuits for efficient transmission of signals such as in an electronic terminating junctor and has a line interface device between telephone lines and electronic networks. The circuit of this invention uses inexpensive and compact parts and is readily and economically manufacturable.
II. Background of the Prior Art
In communications systems such as telephone systems, it is common practice to establish a direct metallic path between a pair of terminal sets for bi-directional transmission of signals therebetween. With a direct metallic path, undesired signals such as transient voltage surges are transmitted along with the desired signals and also the impedances at the interconnected terminal sets must be equal to obtain an impedance match. Impedance matching is oftentimes important, especially when establishing interfaces such as between telephone lines and electronic networks. Conventional transformers may be used for isolation and also to obtain an impedance match, but such are bulky and expensive when low frequency signals such as audio signals are to be transmitted.